1. Field of the Invention
The present invention relates to a copper alloy sliding material and a plain bearing with the sliding material, more particularly a copper alloy sliding material having improved properties of fatigue resistance and anti-seizure.
2. Brief Description of the Art
There has been known a plain bearing with utilization of Kelmet as the copper alloy sliding material. The Kelmet plain bearing has been used for motor vehicle engines and so on, which comprises a back steel, a sintered Cuxe2x80x94Pb system alloy layer provided on the back steel and an overlay layer provided on the sintered Cuxe2x80x94Pb system alloy layer. The Kelmet plain bearing exhibits good anti-seizure property even if the overlay layer is worn out because Pb in the under layer of sintered Cuxe2x80x94Pb system alloy layer is supplied to the sliding-contact surface.
Thus, the known copper alloy sliding materials, typically the Kelmet bearing, have improved anti-seizure property because of a large amount of Pb (i.e. about 20 mass %). While preferably the Pb amount is smaller because Pb adversely affects on the environment, if Pb is reduced, the anti-seizure property is deteriorated since Pb has such an effective function as mentioned above.
On the other hand, in recent motor vehicle engines, bearings tend to be exposed to a higher temperature and a higher specific load because of high rotational speed and high power thereof. However, since the conventional Kelmet bearing contains Pb in a large amount of about 20 mass %, which is soft and has a low melting point, the conventional Kelmet bearing has low strength and poor fatigue resistance especially under a high specific load and has a problem that Pb exposed to a high temperature flows out excessively from its initial points under the sliding-contact with the mating shaft resulting in failure of keeping good anti-seizure property.
The present invention is proposed under the above technical background.
An object of the invention is to provide a copper alloy sliding material and a plain bearing with the copper alloy sliding material, which can have excellent anti-seizure property while reducing the Pb content and further which exhibits good anti-seizure and fatigue resistance properties even under a high temperature and a high specific load.
The present inventors found that the copper alloy sliding material can have improved bearing properties, especially anti-seizure and fatigue resistance properties by providing it with an alloy structure in which intermetallic compound grains are present adjacently to Pb phase islands and/or Bi phase islands. Such a copper alloy sliding material exhibits excellent foreign substance embeddability and excellent anti-adhesion property since the Pb and Bi phases are soft, and has improved wear resistance since the intermetallic compound is harder than the matrix. In the case where there are present hard intermetallic compound grains between the Pb and/or Bi phase islands and the matrix, the sliding material can have improved anti-seizure property, since, under load or due to wear, the surface (bearing surface) of the sliding material has projections at hard intermetallic compound grains 8 and recessions at the soft Pb and/or Bi phase islands 7 and the matrix 6 as shown in FIG. 2 wherein lubricant oil is retained in the recessions. Further, in the case where there are present hard intermetallic compound grains adjacent to the Pb and/or Bi phase islands in the sliding material, Pb and/or Bi, each having the low melting point is prevented from excessive flowing out by the existing intermetallic compounds whereby the anti-seizure property under high temperature is improved. While there is a concern that the soft Pb and/or Bi phase is liable to become a trigger point of fatigue rupture due to cyclic loading, even if cracks were to occur from trigger points of the Pb and/or Bi phase, they are prevented from extending to the matrix by the hard intermetallic compounds whereby the copper alloy sliding material is improved in fatigue strength.
On the basis of the above consideration, according to a first aspect of the invention, there is provided a copper alloy sliding material comprising Pb and/or Bi in an amount or a total amount of 1 to 10 mass % and having not less than 100 of Vickers hardness, wherein intermetallic compounds are present adjacently to the Pb-phase and/or Bi phase, whereby the sliding material has excellent foreign substance embeddability and excellent anti-adhesion property. The copper alloy sliding material has also excellent anti-seizure property and improved wear resistance and fatigue resistance properties without increasing the amount of Pb and/or Bi. Further, since the sliding material has not less than 100 of Vickers hardness, it is improved in the load capacity and also the fatigue resistance property under a high surface load.
According to one feature of the invention, the copper alloy sliding material is a sintering alloy and comprises, by mass percent, 0.5% to 15% Sn, at least one of 0.5% to 10% Ni and 0.1% to 10% Ag in an amount or a total amount of 0.1% to 10%, at least one of Pb and Bi in an amount or a total amount of 1% to 10%, and the balance essentially of Cu. Thus, when sintering the copper alloy sliding material, Pb and/or Bi melts under a high temperature atmosphere to produce a liquid phase of which catalyst effect promotes diffusion of components of the matrix around the liquid phase so as to produce an intermetallic compound at interfaces among the matrix and Pb and/or Bi phase islands, so that there can be produced a metal structure having an intermetallic compound adjacent to the Pb-phase islands and/or the Bi-phase islands.
Here, a description of the alloying elements of the sintering copper alloy will be provided with regard to reasons of those defined amounts and advantageous effects obtainable from the defined amounts.
(a) Sn (0.5 to 15 mass %)
Sn strengthens the alloy matrix thereby improving the fatigue resistance property of the alloy. It also reacts with Ni and Ag in the matrix around the soft Pb and/or Bi phase islands to produce an intermetallic compound. If the Sn amount is less than 0.5 mass %, the matrix strengthening effect thereof can not be obtained. If it exceeds 15 mass %, Cuxe2x80x94Sn system compounds are produced excessively, so that the alloy becomes brittle. Preferably, the Sn amount is 1 to 11 mass %.
(b) Ni and/or Ag (by mass, 0.5% to 10% Ni and/or 0.1% to 10% Ag in an amount or a total amount of 0.1% to 10%)
Ni and Ag produce intermetallic compounds, for example an Nixe2x80x94Sn system or an Agxe2x80x94Sn system, respectively, to strengthen the alloy matrix thereby improving the fatigue resistance property of the alloy. However, less than 0.5 mass % Ni does not form the Nixe2x80x94Sn system intermetallic compound, and less than 0.1 mass % Ag does not form the Agxe2x80x94Sn system intermetallic compound. An excess amount of Ni and/or Ag exceeding 10 mass % in an amount or a total amount makes the matrix too brittle resulting in an unpreferable copper alloy sliding material.
(c) Pb and/or Bi (by Mass, 1% to 10% in an Amount or a Total Amount)
Pb and Bi form a liquid Pb-phase and a liquid Bi-phase during sintering, respectively, to promote the sintering reaction. The liquid Pb-phase and the liquid Bi-phase form soft phases dispersed in the matrix, respectively, to improve foreign substance embeddability and anti-seizure property of the alloy. If Pb and/or Bi is less than 1 mass % in an amount or a total amount, the above properties can not be obtained. An exceeding 10 mass % amount thereof deteriorates strength including fatigue strength of the alloy.
According to another feature of the invention, the copper alloy sliding material further comprises, by mass percent, one or more of Fe, Al, Zn, Mn, Co and P (phosphorous) in an amount or a total amount of not more than 40%, whereby the matrix is strengthened to improve fatigue resistance of the alloy. However, an excess amount of one or more of them exceeding 40 mass % in an amount or a total amount makes the matrix too hard, thereby to deteriorate the conformability resulting in an unpreferable copper alloy sliding material.
According to a second aspect of the invention, there is provided a plain bearing comprising a back metal and the copper alloy sliding material being provided on the back metal. The plain bearing can be used for high speed and high power engines for motor vehicles. When it is applied to such an engine, it exhibits good properties of anti-seizure, wear resistance and load carrying capacity under harsh operational conditions.
According to one feature of the plain bearing, an overlay layer of metal and/or resin is provided on the copper alloy sliding material. The plain bearing is excellent in initial conformability, foreign substance embeddability and anti-seizure property.